On-site-assembly type optical connectors are one example of known devices for connecting optical fibers by abutting end faces of the optical fibers against each other. On-site-assembly type optical connectors are optical connectors being structured to enable easy assembly to optical cable terminals at sites where optical fibers are being laid. An in-built fiber that is already factory-installed is attached to a ferrule of an optical connector before assembly, and an end portion of the in-built fiber is placed in a clamp section (mechanical splicer section). At the site of assembly operations, the end portion of a cut insertion fiber is inserted into the clamp section of the on-site-assembly type optical connector, and the in-built fiber and the insertion fiber are optically connected by the end faces of the in-built fiber and the insertion fiber being abutted against each other in the clamp section and both of the fibers being fixed.
A liquid index-matching material is generally pre-introduced into the clamp section, which serves as the section where the optical fibers are connected, in order to suppress connection loss (see, for example, FIG. 16 of Patent Literature 1). However, sometimes air bubbles remain in the connection section even when the optical fiber connection section is coated in the liquid index-matching material. Thus, in the on-site-assembly type optical connector of Patent Literature 1, a solid index-matching material is pre-set on the end face of the in-built fiber, and the end faces of the optical fibers are connected together through the solid index-matching material (see FIG. 7 of Patent Literature 1).